Earthquakes and volcanoes research

by thalacufiya (student)

Earthquakes

Unexpectedly out of no where, pictures on the wall start wobbling. Pots and jars rattle as if they’ll fall and break into 100’s of pieces. Paint, dust and wood start dropping from the roof. You don’t know why but unpredictably you start quivering as well. It feels as if someone picked up your land and was gently shaking it. If you have no idea what I’m talking about, well you’ve just experienced one of natures most violent phenomena, an earthquake. While such a mild earthquake described above happens often around the world, the people of Northridge, California, will never forget that morning when an earthquake happened to them. It was 4:30 am, 1994 when a huge rock 11 miles under the city suddenly jolted upwards. Cracks opened in the ground and bridges snapped like toothpicks. Gas lines broke and started fires! This earthquake lasted 30 seconds but caused 57 deaths and 9000 injuries and left thousands homeless. Now what do you think about earthquakes?

What is an earthquake?

Although we can’t feel it, the earth is squeezing, pushing, and pulling beneath our feet. Scientists have discovered that just like a jigsaw puzzle, the earth has many plates that fit together but instead of keeping still, they move. Earthquakes are caused by these tectonic plates, moving under the earth’s surface. Forces inside earth’s surface slowly bend, twist and turn the rock in earth’s crust. These movements send shock waves shooting through the surrounding rocks in all directions and the ground on the surface shakes. Sometimes the strain becomes too great and the plates shoot past one another, breaking off pieces as they do.

Lets take an inside look

Plate boundaries

The places where plates meet are called plate boundaries. At some boundaries, plates move easily past one another, or collide and scrunch up to form mountains or even form volcanoes. Most earthquakes happen at the boundaries of an earthquake

Divergent Boundary-

At divergent boundaries tectonic plates move away from one another. In many cases, magma rises from the mantle to fill in the gap or one plate slides down to fill in the space. These types of earthquakes usually occur in the ocean (Mid-ocean ridge) not very deep in the earths crust and are not very powerful.

Convergent Boundary

Convergent plate boundaries arise when tectonic plates of equal or differing densities collide. If the plates have equal density, the collision causes an orogeny like the Himalayas. Mountains shoot up relatively quickly in this process over the past few million years. Convergent boundaries begin deep in the earths crust and are strong and destructive.

Transform Boundary

Transform boundaries slide past one another horizontally. The tension builds with the sliding of these plates along one another until the tension releases and there is a sudden "jump" between plates thus causing an earthquake. Most transform boundaries are on the ocean floor.

Faults

This crack earns a special name once the rock along a crack has moved: fault. Faults are cracks or fractures in the earth's Lithosphere caused by stresses created by the movement of tectonic plates. Some faults called surface faults can be seen from the ground such as the San Andreas Fault in California. Others, called blind faults, lie beneath the surface. During an earthquake, one side of a fault slips. There are quite a number of earth faults divided into categories determining on the way they slip. There are three major types of faults: strike-slip, normal, and reverse

Normal Fault

Plates are pulled apart and one side moves down. Normal faults usually occur at divergent plate boundaries.

Reverse Fault

The plates push together while one side moves up. Reverse faults happen at convergent boundaries.

Strike slip Fault (or transform fault) One rock moves up and over another. These faults usually occur where plates are being “sub ducted”

Seismic Waves

Seismic Waves are basically waves of energy that are released in waves from the focus, or place beneath the earth’s surface where the rock first breaks. They are the energy that travels through the earth like a pebble dropped into water, spreading away from the focus.

As seismic waves spread, they often make the ground vibrate. They also vary in speed depending on the type of rock or other material they are passing through.

There are several different kinds of seismic waves, and they all move in different ways. The two main types of waves are body waves (which include P waves and S waves) and surface waves (which include love waves and Rayleigh waves). Body waves can travel through the earth's inner layers, but surface waves can only move along the surface of the planet like ripples on water.

Body Waves

Body waves are the first type of seismic waves released during an earthquake. Body waves have little effect on Earth’s surface. There are two types: P-Waves and S-Waves.

P-Waves (Primary or compression waves)

This is the fastest kind of seismic wave. P waves can move through solid rock and fluids. These waves push and pull the rock as it moves through just like sound waves push and pull the air. Usually we only feel the bump and rattle of these waves.

S-waves (secondary waves)

An S wave is slower than ...